Power problem!!

[oldsman003]

Quick rundown
Ribs great plenty of power under 2k rpm. Above that cruising after about 5 minutes of 50mph plus driving truck will fall on its face when you give it throttle. Anything more than a fraction of throttle will act like the truck just stops.
Ive replaced plugs and wires checked for vacuum leaks, new fuel filter as well.
Seems like it happens more the longer the truck runs as if the warmer it gets, I can drive it 10 min down the road 55mph and under wroth no trouble, get ir on the freeway athe 65 for 5 minutes and starts bogging out almost starving when I put my foot on the throttle.

 

[iamdub]

Any codes? I'm betting on clogged cat or dying fuel pump, but leaning more towards fuel pump. I believe you can borrow a fuel pressure tester from Autozone for free. I don't know the specs exactly, but they're gonna be something like 60psi with key on/engine off, 55psi when running, etc. If someone else doesn't reply with the specs, I'm sure a little Googling will find them.

 

[oldsman003]

I have debated testing the pressure, it is straight piped with no cats because that was my initial thought was cats because I had that issue with my previous 04 xl. I myself feel that a fuel pump either works or doesn't ya know which is kind of why I have yet to test it and I'm not exactly sure how to test whilst driving.. But testing pressure at idle and driving would be the tell tale.

 

[oldsman003]

I mean the truck has 362k and climbing, and I have no idea on maintenance. I had to clean and replace a few injectors when I bought it. And now I still get a flashing check engine light while driving under any conditions. No codes get stored just a misfire flash

 

[Tonyrodz]

I have debated testing the pressure, it is straight piped with no cats because that was my initial thought was cats because I had that issue with my previous 04 xl. I myself feel that a fuel pump either works or doesn't ya know which is kind of why I have yet to test it and I'm not exactly sure how to test whilst driving.. But testing pressure at idle and driving would be the tell tale.

A fuel pump can slowly die, doesn't have to be all of the sudden. Symptoms can be no power, running like crap. First test would be to see where the pressure is at idle. You could hook the gauge hose to the shrader and hopefully the hose is long enough to run the gauge to the windshield and put it under the wiper and take it for a drive. See what you have and go from there.

 

[rockola1971]

Rev the engine up to copy what happens at driving RPM. The fuel pump doesnt know the difference between drivetrain loaded up wheels on the ground vs just sitting in park and revving up. Check the fuel pressure. Are you getting specific bank or cylinder misfire codes? Long shot that you may have ignition coils giving up the ghost.

 

[iamdub]

As was said, fuel pumps most certainly don't always "work or not work". It can get weak just like any other electric motor. Also, the wiring harness connector on the older trucks is a known weak spot so GM upgraded the design. This fixes the connecting point, but the wiring itself is borderline adequate for the amperage. Aged wiring and/or a weak connection will cause a drop in the voltage feeding the pump. The drop in voltage makes the pump pull more amperage, which is even more amperage through that aforementioned borderline adequate wiring. More amperage makes the pump run hotter, more heat makes the pump pull more amperage, and the downward spiral continues. The truck running poorly after a length of time is concurrent with the pump heating up and getting weak.

Most fuel pressure gauge sets I've used have hoses long enough to do as Tony mentioned, but there's no need to test the pressure while driving. Hook up the gauge and test with key on/engine off, engine running at cold start, engine running after X amount of time, etc. If it were me, I'd go for a drive near home and come back and test when it acts up again.

Of course, it may not be the fuel pressure. But, the symptoms definitely are those of a failing pump and it would be a simple one to rule out before digging deeper. Weak fuel pressure can cause misfires. Other than the misfire flash, your CEL is never on? Is your truck tuned/fooled (non-foulers, O2 sensor simulators, etc.) for the deleted cats?

 

[SnowDrifter]

Couple things that come to mind in no particular order

Do you have codes?

Fuel pressure regulator or fuel pump. Grab a pressure tester. These are super easy, there's a port on the passenger side of the fuel rail under the engine cover

Coil packs can sometimes work fine when cold but start to fail when they get hot. Easiest way to check this is with a heat gun or blow dryer

Carbon buildup in intake raising your compression ratio. Easy way to see is to fill with the highest octane gas you can get your hands on

MAF. Pull it apart, look for burnt resistors and clean with MAF cleaner

Oxygen sensors could be going bad. You'll see this particularly when the car is warm. Long story short the computer doesn't use the oxygen sensors until your engine is warm. Need a scan tool with live data to check or an accurate multi meter.

I very much doubt it would be knock sensors causing the computer to pull timing. It's a 1 wire microphone. It works, or it doesn't.

 

[oldsman003]

I have cleaned the maf, looked great

It absolutely will not stumble in park revving. I wish it would but it doesn't.

The flashing s.e.s. is only while driving

No stored codes

Weird because I'm running open cats I figured to expect an O2 code but there isn't.

 

[bottomline2000]

I have cleaned the maf, looked great

It absolutely will not stumble in park revving. I wish it would but it doesn't.

The flashing s.e.s. is only while driving

No stored codes

Weird because I'm running open cats I figured to expect an O2 code but there isn't.

Flashing SES is saying the engine has a condition that could be harmful to the engine or emissions system. Since u don't have cats no need to worry about them but chances are your pump is failing causing a lean condition that WILL harm your engine.

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